Currently, zooming of images is implemented by providing an input for changing the scale of the viewed area. Various implementations are possible. For example, in a 2D image, the user may select the zoom center (i.e., a fixed point in the 2D image) and scroll the mouse wheel to magnify or reduce the image. For mammography, this is typically combined by the display of mirrored images and mirrored pan and zoom operations as described in WO 2006/018816 entitled “Display system for the evaluation of mammographies”. Two-dimensional (2D) image zooming can be generalized to three-dimensional (3D) image zooming. For example, for perspective projection, the displayed images are zoomed when the camera moves along the line towards one of the vanishing points. For orthogonal projections, zooming is based on changing the scale in the planes perpendicular to the projection lines, i.e., perpendicular to the viewing direction.
The drawback of available zoom implementations is that, when a user views an image region which is of interest to him, the zooming function does not always keep that region in the display. The region may quickly disappear from the display when the zoom center is fixed far away from the region of interest and the region of interest is close to the border of a viewport for displaying the image. This problem is often addressed by selecting the zoom center in the center of the region of interest. However, this method fails when the region of interest is adjacent to the border of the viewport.